"The living bacteria, plucked from an altitude of 10 miles (16 km) or higher by a scientific balloon, could have been deposited in terrestrial airspace by a passing comet, according to the researchers. The microorganisms are unlike any known on Earth, but the astrobiologists 'want to keep the details under wraps until they are absolutely convinced that these are extraterrestrial,' said study participant Chandra Wickramasinghe, a noted scientist at Cardiff University in Wales."